“Breast-feeding is one of the most cost-effective interventions for improving maternal and child health,” said Dr. Georges C. Benjamin, executive director of the American Public Health Association.

The American College of Obstetricians and Gynecologists “strongly supports” breast-feeding and says evidence of benefits “continues to mount.” Global health experts say that in poor countries in particular, breast-feeding reduces diarrheal diseases and saves babies’ lives.

Global health experts said the president’s stance suggested a lack of knowledge about breast-feeding and the history of the marketing of powdered formula to poor women in developing countries. Powdered formula mixed with unclean water can be dangerous for babies. The deaths of babies who had been fed infant formula led to a boycott starting in the late 1970s against the Nestlé corporation, a major formula producer.

“Malnutrition and poverty are the precise settings where you absolutely do need to breast-feed, because that’s the setting where access to safe and clean water for reconstituting powdered formula is often impossible to find,” said Dr. Michele Barry, senior associate dean for global health and director of the Center for Innovation in Global Health in the Stanford School of Medicine, in response to the president’s tweet.

Dr. Barry said malnourished mothers in poor countries still produce healthy breast milk, though they may not be able to make enough,but are unlikely to have access to clean water for reconstituting powdered infant formula. In wealthier countries, poor women who do have access to clean water often dilute expensive formula to make it last longer, which can also cause malnutrition.

While some women are unable to breast-feed, cannot make enough milk, have medical conditions that prevent them from breast-feeding, or choose not to, the consensus of most mainstream medical organizations is that “breast is best” when it comes to infant nutrition and health. Breast milk provides essential nutrients as well as hormones and antibodies that protect newborns against infectious disease.

A report by the federal Agency for Healthcare Research and Quality analyzed the available evidence on breast feeding and found that breast-fed infants had significantly fewer respiratory tract infections during their first year of life, a 50 percent decrease in ear infections, and a 64 percent decrease in gastrointestinal infections. For premature infants, breast milk is considered critical because it lowers their risk of developing necrotizing enterocolitis, a dangerous condition that can destroy the wall of the intestine.

Breast-feeding is also associated with a lower risk for sudden infant death syndrome; allergies, including conditions like asthma and eczema; celiac disease and childhood inflammatory bowel disease.

Children who were breast-fedhave lower rates of Type 1, or juvenile, diabetes, and of two types of leukemia. They also have lower obesity rates, though the link may be a result of higher educational and income levels among many breast-feeding mothers in the United States.

The report also noted that breast-feeding makes economic sense: Researchers who ran a cost analysis reported that if 90 percent of mothers in the United States breast-fed exclusively for six months, there would be savings of $13 billion per year.

Babies aren’t the only ones who appear to reap health benefits from breast-feeding; research has found that mothers who breast-feed also enjoy better long-term health. They are at lower risk for breast and ovarian cancers, Type 2 diabetes and rheumatoid arthritis. Breast-feeding may also promote heart health and healthy blood pressure.

More recent studies have found that mothers who breast-feed are at lower risk for developing aggressive hormone receptor negative breast cancers and that those who had gestational diabetes during pregnancy are less likely to go on to develop diabetes later in life if they breast-feed.

A version of this article appears in print on , on Page A13 of the New York edition with the headline: Medical Experts Criticize Trump’s Stance on Breast-Feeding and Formula. Order Reprints | Today’s Paper | Subscribe